In legged mobile robots, in particular, in biped mobile robots, the floor reaction force detector such as a six-axis force sensor is used to detect the floor reaction force acting on the robot from a floor surface which the robot contacts and based on the detect a floor reaction force, control is appropriately conducted to achieve stable walking. In order to improve detection accuracy, the floor reaction force detector should preferably be installed at a position close to a floor contact end of the feet. In view of this, a technique mentioned in Japanese Laid-Open Patent Application No. 2000-254888 proposes to install the floor reaction force detector at the sole of foot such that the floor reaction force detector contacts a floor surface directly.
However, in this prior art, since the floor reaction force detector contacts a floor surface directly, it has a drawback that rigidity of the detector need be enhanced. The feet of legged mobile robots, in particular, biped mobile robots should preferably have not only appropriate rigidity enough for enabling to maintain a stable posture during standing, but also appropriate elasticity for enabling to absorb and mitigate the impact at landing of a free leg.
Accordingly, if the feet of the prior art are given appropriate rigidity, from the necessity of structure, a portion above the floor reaction force detector, i.e., a portion close to the robot body must have elasticity. However, if the portion above the floor reaction force detector is provided with elasticity, since the floor reaction force to be detected by the floor reaction force detector is absorbed by that portion, the detected floor reaction force may differ from the force that actually acts on the robot, thereby disadvantageously degrading the performance of control mentioned above.